Shock absorbers are used in downhole applications to protect equipment in the well if a tool string is accidentally released. The kinetic energy of the falling string or other object is dissipated by a shock absorber to reduce or eliminate damage from impact.
In some designs for downhole, relative movement crushes material in the absorber or radially deforms one member as another with an interference fit is forced into it or simply uses a sharpened tungsten carbide element to rip into a telescoping tube. These designs and variations of them are illustrated in U.S. Pat. Nos. 6,454,012; 6,109,355; 6,708,761; 3,653,468; 3,949,150; 4,679,669; 4,693,317; 4,817,710 and 4,932,471. U.S. Pat. No. 5,875,875 relates generally to shock absorbers in unrelated industrial applications such as vehicles, machinery and buildings. It stays away from using liquids and gasses claiming that the cost of precision machining and seals that pneumatic or hydraulic designs entail makes them cost more to fabricate and maintain. Instead it focuses on foams and other materials that can stay in a cavity without seals until the absorber is actuated.
Yet another design for downhole use forces a plunger into a housing and creates an exit flow path to a port for the mud in the housing as the piston top gets further away from the ports. In this manner the resistance to piston movement progressively increases the greater the relative movement between the piston and its surrounding housing. This design is described in U.S. Pat. No. 5,183,113.
It is also worth noting that the design in U.S. Pat. No. 6,109,355 features a leading end 18 made of brass so that it can take the initial impact and dissipate it. The nose 18 features a flow path into the tool string.
The present invention provides a shock absorber that uses well fluids. It is held in the run in position until it receives an impact that creates relative movement. As a result the volume of a fluid chamber preferably filled with incompressible fluid and temporarily retained by a breakable member is reduced as the fluid is forced through an orifice and into the surrounding wellbore. The initial impact is absorbed by a nose intended to be crushed using voids designed to allow it to collapse on itself on impact. These and other features of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings that appear below while recognizing that the claims define the full scope of the invention.